Benefits of Greenroofs
Greenroofs are widely considered the best management practice
to reduce pollution in cities. A standard construction practice in
many countries for hundreds, if not thousands, of years, greenroofs
are common practice in Europe today and represent a fast-growing
opportunity in the US and Canada.
Greenroofs provide many of the same benefits as trees in areas
where planting trees is limited or not possible. A Casey Trees and DC
Greenworks study estimated a 56% reduction in rooftop run-off in DC’s
commercial core if 80% of rooftop space were greened. Research also
shows that greenroofed buildings reduced daytime roof temperatures
as high as 155oF to ambient air temperature, creating significant energy
savings, air quality improvements, and roof longevity.
Vancouver, BC Library
Photo courtesy: Landscape Architecture Magazine
Public Benefits
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Rockefeller Center, New York
Photo courtesy: Garland Company
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Reduce stormwater infrastructure costs for larger pipes
& tunnels to handle combined sewer overflows (CSOs);
DC is considering a $1.25 billion Long Term Control Plan
to manage its CSOs.
Reduce ambient air temperatures and Heat Island
Effect: Like urban forests, greenroofs absorb and/or
deflect solar radiation to reduce heat. The resultant
cooling slows and reduces the chemical processes that
produce ground level ozone, nitrous oxides and smog.
Air Cleaning: Like trees, greenroofs filter out fine,
airborne particulate matter as air passes over the plants
and absorb gaseous pollutants through photosynthesis.
Provide Open Space & Visual Amenity to relieve stress.
Habitat Creation for birds, bees, and butterflies.
Private Benefits
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Chiropractic Center, Hazelton,PA
Photo courtesy: Emory Knoll Farms
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Energy Savings: A Chicago energy study estimated
peak demand would be cut by the equivalent of one small
nuclear power plant if all the city’s roofs were greened.
Moderate roof temperatures and fluctuations extending
roof membrane life from 2x-5x as long and reducing
maintenance.
Sound Insulation: Tests show that 12cm (5”) of growing
medium alone can reduce sound by 40db.
Lower Stormwater Utility Fees
Receive energy tax credits, grants, and subsidies
Increase floor-to-area ratios for builders in many cities.
Increase property values and revenue producing
opportunities from increased usable space.
Greenroof Opportunity to
Re-Green DC
Sample Downtown Area, Washington, DC, 2002
Projected Downtown Area, Washington, DC, 2020
if 80% of roofs were Greenroofs (Note: avg. life of
commercial roofs in DC is 10-20 yrs.)
Thermal Map of Washington, DC
Dr. Karen Liu, National Research Council, Ottawa
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A 3” Greenroof will hold
at least 3/4” of rain and on
average up to 2”.
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Based on DC’s average
rainfall, if 80% of commercial
rooftop space were greened,
rooftop run-off would be
reduced by an estimated 56%.
The Greenroof at 1425 K Street
800 sf
Greenroof Area
Plant Species
Bloom
Color
Winter
Interest
Delospema nubigenum
Yellow
Yes
560
Pink
Yes
140
White
Yes
1,750
Pink
No
490
Sedum kamts chaticum
Yellow
No
910
Sedum reflexum
Yellow
No
700
Sedum sexangulare
Yellow
Yes
1,750
Orostachys bohmeri
Penthouse
W
Sedum album
tA
ve
.N
Sedum Coral Carpet
Ve
rm
on
1000 sf Research
Control Area
2,700 sf
Greenroof Area
Patio
No. of
plants
Sedum sieboldii
Pink
No
210
Sedum spurium Fuldaglut
Red
Yes
1,260
Sedum spurium ‘John Creech’
Pink
No
700
Sedum Weihenstaphaner Gold
Yellow
Yes
1,260
TOTAL
K ST. NW
Building Footprint with Total 3,500 sf Greenroof
Research and Monitoring Stations will collect
information about air and roof membrane temperatures.
One weather station will be located in the control area
and the other in the greenroof area on the east side of
the penthouse. Bob Ryan Chief Meteorologist for NBC4
donated one of the stations and will report data.
Greenroof Profile (Previously IRMA Roof)
(16-20 lbs/ sf, fully saturated & with snowload)
($14.43/ square foot)
9,730
The Greenroof at 1425 K Street
1425 K Street Greenroof Costs
The cost of a green roof varies based on a number of factors:
• Type of Green Roof
Extensive green roofs (soil depths of 2-3”) cost significantly less that
intensive green roofs (soil depths of at least 6” and greater plant variety)
• Type of Construction
New - most cost effective when planned into the initial roof design
Replacement - incremental costs minimized because conventional roof
needs to be replaced anyway
Retrofit - the least cost effective option
• Economies of Scale
Casey Trees Volunteers and D.C. Greenworks staff
during Greenroof construction, June 2004
The 1425 K Street Greenroof
was a 3,500-sf retrofit and
one of the first green roofs in
the region. The research and
demonstration project was
funded by a total of $60,000 in
grants from the Chesapeake
Bay Small Watershed Grants
Program and from the Watershed Protection Division of
the DC Department of Health.
The grants funded construction
costs, public outreach, signage, maintenance, research
and monitoring.
The cost per square foot of green roof decreases as the total green roof
area increases. As demand for green roof materials, contractors, and
design professionals increases, green roof costs will decrease.
Greenroof Construction Item
Permitting, Insurance, Bonding
Roof Membrane with Root Barrier & Hoist
Leak Detection System
Drainage Course
Soil Media
Erosion Blanket (Jute Mat)
Plants
Tools & Equipment
Labor for Installation
Total Cost (3,800 sf work area)
Cost
$2,156
$26,024
$4,200
$4,275
$2,825
$331
$4,778
$3,615
$6,646
$54,850
$14.43/sf
The Greenroof at 1425 K Street was
made possible by:
DC Greenworks brings ideas, expertise, and tools to empower urban
communities to improve their natural and built environment. We actively
promote and deliver cutting-edge solutions that are cost-effective,
eco-friendly, and socially benefiicial. www.dcgreenworks.org
The mission of Casey Trees Endowment Fund is to restore, enhance,
and protect the tree canopy of our nation’s capital. Our vision is to
make our nation’s capital a model green city. www.caseytrees.org
Blake is a real estate company dedicated to providing superior service
and the highest quality projects that consistently exceed our clients’
expectations through innovation, teamwork, creativity and experience.
www.blakereal.com
National Fish and Wildlife Foundation, Chesapeake Bay Small
Watersheds Grants, provides grants to organizations working on a
local level to protect and improve watersheds in the Chesapeake Bay
basin, while building citizen-based resource stewardship. $35,000.
www.nfwf.org
The mission of the Environmental Health Administration is to prevent
and control environmentally related diseases while protecting and
preserving the ecological system in the District of Columbia. $25,000.
www.dchealth.dc.gov/about/index_environmental.shtm
EPA’s mission is to protect human health and the environment.
Through its Offices of Water and Technology Innovation and
Superfund - Community Involvement, EPA helped fund the
greenroof installation and Covenant House Youth workforce training.
www.epa.gov
CHW’s is a faith-based, social service organization whose mission is
to serve suffering children of the street and to protect and safeguard
all children in Washington, D.C. www.covenanthousedc.org
Commercial Roofing and
Sheet Metal Company
International Leak
Detection, Electronic Field
Vector Mapping
www.leak-detection.com
Barrett Roofs
www.barrettroofs.com
J-Drain, Greenroof
Drainage System
www.j-drain.com
Laurel Valley Soils
www.laurelvalleysoils.com
Emory Knoll Farms /
Greenroof Plants
www.greenroofplants.com
Bob Ryan, sponsored research
station and greenroof reporting.
www.nbc4.com/weather
Bridges to Friendship
www.earthvision.net/
bridges/strplnfl.htm
LID Center,
Monitoring Plan Consulting
www.lowimpactdevelopment.org